The invention relates to a shifting device for pinion gear change transmissions.
To shift pinion gear change transmission, selector forks are used, as a rule, in order, by means of transmission devices, to transmit shifting movements from a shift lever to the positive-fit couplings of the transmission. The shifting movements are transmitted to the shift lever according to known H gear shift patterns. The transmission device must have few transmission losses and small volume and be well damped to ensure the shifting comfort required in modem vehicles. It must reliably prevent the possibility of several gears being simultaneously actuated. One other function is the conversion of the shifting movement on the shift lever (path and force) to the path and force needed by the arrangement of the positive-fit couplings on the output shift and/or countershaft and the configuration thereof in the form of dog clutch control or synchronizer units.
Shifting devices of this kind can be divided in the following sub-groups:
Selector forks for transmitting the shifting force to the sliding sleeves of the positive-fit couplings. The positive-fit couplings, often synchronized, are as a rule disposed on shafts of the transmission and selectively connect pinions with the shafts. Selector forks transmit the shifting force to the sliding sleeves by sliding bearings. This requires a wear-resistant material. To keep the weight and costs low, selector forks are often made of die-cast aluminum or compound material and in place of the low-friction bearing is a sprayed molybdenum or provided with crossheads shoes. In the gear shift mechanism with a central shifting rail proposed, e.g. in U.S. Pat. No. 4,621,537, the gate selection and gear shift demand precise machining and hardened edges directly on the selector fork. This requires different costly selector forks made of malleable cast iron. Another disadvantage of this design is the many low-friction bearing places between central shifting rail and selector forks which mainly when cold can lead to tough selection and shifting.
Longitudinal guides for transmitting the shifting force to the selector forks. Two basic principles are known:
a) rails firmly connected each with one selector fork. The rails slide in the transmission housing and transmit only forces in the longitudinal direction. There are rails made of pipes, round steel, or as stamped or bending parts.
b) a central rail which slides in the transmission housing and transmits longitudinal and rotational movement. All selector forks slide on the rail. The choice of which selector fork is to be coupled with the shifting rail for shifting and the locking of the non-actuated selector forks in this neutral position in longitudinal direction are effected by shaped and locking parts between shifting rail and selector forks.
Gates and gear shift make possible the selection of the gate in which lies the desired gear and the shifting of the gear by moving the shift lever. Three basic principles are known:
a) selection and locking between the central rails and the selector forks such as shown in EP 0 395 241. At the same time, strict requirements are imposed on the selector forks in relation to precise machining and strength of the material. This results in expensive machining and great weight. Many friction places generate which can have a negative effect upon the shifting comfort.
b) selection of the desired shifting rail by shifting finger or lever fastened upon a separate selection shaft. The gears are locked by separate means such as pins and balls or pawls between the selector forks and shifting rails. This type is often used in pinion gear change transmissions of passenger cars and light industrial vehicles.
c) selection and locking by a so-called switching comb. The switching comb consists of several flat segments of which alternatively one is connected with a selector fork and one firmly connected with the housing in shifting direction. The shifting finger that slides through said switching comb can only actuate the desired gear when its position coincides in shifting direction with the flat segment of the selector fork. In other positions, the selector forks remain locked. Such a shifting system is shown by way of example in DE 30 00 577 C2. The shifting device is often used in transmissions of commercial vehicles.
Connection of different switches and sensors to indicate the transmission situations (for ex., neutral position reverse gear, etc.).
Connection of different selector units. For different vehicles different selector units are used such as lever shifts, turning-shaft shifts, cable-controlled and hydrostatic shifting mechanisms. To make possible installing on a pinion gear change transmission different selector units, a unitary interface must be obtained between pinion gear change transmission and selector units.
Due to movements of the sliding sleeves or jerks on the vehicle the shifting parts can be excited in a manner such that an engaged gear trips during the drive. To prevent this, the shifting parts of each gate are fixed by means of spring-loaded detents in the xe2x80x9cneutralxe2x80x9d and xe2x80x9cgear inxe2x80x9d positions. This constitutes an added expense, since a separate detent of the positions again takes place in the selector unit.
It is often necessary in pinion gear change transmissions to construct different ratio series, so-called high gear or direct gear designs. Here the low-loss direct lock-up clutch, e.g. in a 5-gear transmission is the 4th gear in the high gear transmission and the 5th gear in a direct gear transmission. This requires, e.g. a reversal of shifting direction of the selector forks concerned. In shifting systems with central shifting rail, this is not possible and in shifting systems with several shifting rails, it involves substantial cost. The change of the gear shift pattern, e.g. for right-hand and left-hand steering, is also very expensive in the gear shifts with central shifting rail.
The problem on which the invention is based is to indicate a gear shift device which makes possible that the selecting and shifting forces are transmitted with low friction, reliably and economically between different selector units and the sliding sleeves of the separating clutch. The device should offer simple possibilities of designing gear shift for direct and high gear transmissions and different gear shift patterns, and a clear modulation of the gear shift sections.
The problem is solved with the shifting device for pinion gear change transmissions of the present invention.
In the inventive shifting device, all selectorforks are guided by means of a longitudinal guide firmly connected with the housing parts and actuated by profiled metal plates sliding on said mechanism. The profiled metal plates slide on their other end into a switching comb fastened upon the longitudinal guide and having locking plates as teeth. Between the teeth a shifting finger and an automatic locking device are displaced by shifting means and either interact with the profiled metal plates for shifting the gear or block with the locking plates the non-shifted gates and gears.
In an advantageous embodiment, the longitudinal guide has a profile in the shape of a triangle which consists of a rolled or drawn metal pipe.
In another advantageous embodiment, the selector forks are made of die-cast aluminum or compound material and the guide between the longitudinal guide and the selector forks is integrated directly in the selector fork.
In another advantageous embodiment, the selector forks have plugged-in low-friction bearings.
In another advantageous embodiment, the selectorforks have rollers as longitudinal guide.
In another advantageous embodiment, the profiled metal plates are fixed in shifting direction with the selector forks by means of driver pins and the position of the profiled metal plates in selecting direction is determined by means of spacer discs.
In another advantageous embodiment, the profiled metal plates are connected with positive fit with the selector forks by means of lugs and their position in selecting direction is obtained by outward begins and passages of the profiled metal plates.
In another advantageous embodiment, the selector forks have beneath the longitudinal guide pockets in which mesh the levers supported in the longitudinal guide, the other end of which levers meshes in pockets of the profiled metal plates to reverse the movement of the profiled metal plates.
In another advantageous embodiment, the switching comb is formed in selecting direction alternatively by locking plates and profiled metal plates fixed in shifting direction and in which pockets are situated through which in selecting direction slide the shifting finger and the automatic locking device.
The selector forks are made, e.g. of die-cast aluminum and slide on a longitudinal guide. They have sliding faces which for the actuation of the sliding sleeves are sprayed, e.g. with molybdenum. The longitudinal guide can have different profiles. It can also be part of the transmission housing, since its only function is to guide the selector forks. The sliding bearing of the selector forks on the longitudinal guide can be of different kinds. A specially simple and low-cost solution is a steel pipe drawn and inserted in the transmission housing and holes for guidance into the selector forks. If special requirements are imposed on easy motion, low-friction bearings or all kinds of longitudinal roller bearings between selector forks and longitudinal guide can be advantageously used. When the sliding sleeves have equal mating dimensions, the same selector forks can be used for all or several gears. By virtue of the longitudinal guide no outwards openings are formed in the transmission housing. This reduces the danger of leakage. It also can be advantageous, e.g. to place on the longitudinal guide bolts of the transmission housing.
The selector forks have cams or pins in each of which are profiled metal plate is plugged in or suspended. The profiled metal plate leads by one end to the so-called switching comb where the gear is selected. The non-actuated gears can be locked in a reliable and simple manner by an alternative arrangement of locking plates and profiled metal plates in the switching comb. By means of the profiled metal plates, it is possible to change the sequence of the selector forks in the transmission and also to align them relative to different shafts to determine the sequence of the gear shift pattern. It is thus possible to design the selector forks in the sequence 4-3, 2-1, R-5 and the gear shift pattern with 1-2, 3-4 and 5-R.
If it is needed to reverse a selector fork, one profiled metal plate is fastened upon the lever instead of upon the selector fork. The lever is supported in the longitudinal guide and by its other end actuates the particular selector fork sliding on the longitudinal guide.
Across the profiled metal plates slides a sliding member which is moved in selecting direction by the shifting finger.
Between each profiled metal plate in the switching comb, if there is placed, fixed to the transmission housing in shifting direction, one locking plate in which slides the sliding member, then all non-selected gears are fixed in their neutral position in an easy and economical manner. If the profiled metal plates are situated directly side by side without locking plates, it is also possible to use the known locking means (pins, balls, pawls).
The xe2x80x9cneutralxe2x80x9d and xe2x80x9cgear-inxe2x80x9d fixing occurs only in the selector unit. This is possible since non-shifted gears are fixed by the sliding member. The cushioning of the neutral position is moved in the shifting unit in order to be able better to respond to the different requirements of the respective selector unit and to the customer""s desires. For the above reasons, the cushioning of the gate is also displaced in the selector unit.
It is particularly advantageous with regard to the assembly to fasten the switching comb on the longitudinal guide. Thereby it is possible separately to assemble and adjust the complete shifting system in order then to use it as module in the assembly of the transmission. The position of the switching connection is changeable mainly to be able to react to the conditions of the vehicle in lever shifts. To a great extend, this is possible due to the different shapes of the profiled metal plates.